This invention relates to an ink agitator and more particularly to a non-rotating wedge shaped ink agitator.
In printing presses it is customary to form an ink fountain or reservoir between the fountain roller and the ink fountain blade. There is a metering nip or gap between the ink fountain blade and the ink fountain roller which controls the amount of ink metered onto the ink fountain roller.
It is customary to provide in the ink fountain an ink agitator which mixes the ink within the ink fountain and helps insure an even distribution of the ink within the ink fountain. Traditionally, the major use of ink agitators has been for sheetfed printing presses rather than for web presses. This is because, generally speaking, sheetfed presses use inks which are more viscous the web presses. The more fluid ink used in web presses did not demand the use of ink agitators. In addition, where web pressures were hand fed, ink agitators were not favored since they required periodic cleaning requiring an additional difficult and time consuming maintenance task.
Recently there has been an increase in the use of web presses and the use of ink agitators has increased substantially because of the trend towards stiffer and/or more viscous ink.
Similarly, more and more sheetfed printers have been equipping their presses with ink agitators. Accordingly, there has been an increase in demand for ink agitators.
There are five reasons why agitators are used.
1. To prevent ink skinning. PA1 2. To maintain an adequate supply of ink to the metering nip. PA1 3. To maintain a uniform distribution of ink along the length of the fountain. PA1 4. To work the ink so as to improve its flow characteristics on the rollers. PA1 5. To mix the ink contained in the fountain.
Ink skinning refers to the formation of a partially dried film or skin on the surface of the ink. Although this occurs much more rapidly on sheetfed presses, where inks used dry by oxidation, the problem also exists on commercial web presses which utilize heatset inks. Aside from resulting in ink waste, skinning is undesirable because the skin can break up and generate hickeys, which in turn can result in significant paper waste and loss of productivity. A properly designed ink agitator eliminates skinning by continually stirring the ink and creating new surface without a skin.
Proper operation of an ink fountain requires that an adequate supply of ink be fed to the metering nip. However, the ink has a tendency to back away or hang back from the fountain roller and form a crevice adjacent the roller. This eventually may result in lack of ink at the nip even though there may be sufficient ink remaining in the fountain. A properly designed ink agitator will maintain the ink in contact with the ink fountain roller.
An ink agitator can also help prevent starvation of the metering nip in areas of heavy ink coverage which can adversely reduce print density. When the ink is not free to flow along the length of the fountain, there can occur ink shortages in areas where more ink is used particularly where less fluid inks are used. A poorly designed ink agitator will push or plow ink towards the ends of the fountain thus aggravating the problem.
The fourth reason for using an ink agitator is because it results in working of the ink contained in the fountain, thereby reducing the tack of the ink transferred to the ink rollers. Although the actual working of the ink is effected by the fountain roller rather than the agitator, the agitator makes this possible by constantly pushing the ink into contact with the roller.
Another reason for using an ink agitator is its mixing ability which prevents sudden changes in the composition of the ink fed to the metering nip which could cause sudden and drastic changes in print density. Sudden changes in the ink composition can occur because of fresh ink added to the ink fountain to compensate for consumption; paper lint, emulsified ink, or ink bleed from previous down colors, all which may be carried into the fountain by the ink which is fed back from the roller train.
The prior art teaches a variety of different types of ink agitator devices. One commonly used design consisted of one or more narrow blade-type fingers located close to the fountain blade normal to the roller. The fingers reciprocate parallel to the axis of the roller. In addition, other agitator structures have been tried including a plow-shaped traversing finger, and vertical rods designed to longitudinally slice the ink wave generated by the conventional blade-type finger. Another agitator utilized two oscillating arms, placed in the bottom of a box-type fountain.
None of these proposals were completely satisfactory in that they were difficult to clean and sometimes caused plowing of the ink to either end of the fountain. More recently, a pyramid shaped traversing member has been used with some success on small duplicator-type presses.
The most commonly used ink agitator utilizes a rotating conical shaped member which is positioned in the ink fountain substantially normal to the fountain roller, with less than 1/16 inch clearance between it and the fountain blade. The cone is attached to an actuator which causes the cone to traverse back and forth along the length of the fountain. As it traverses back and forth, the cone also rotates in an anti-rolling direction. In other words, the cone shaped agitator is rotated in the opposite direction than it would rotate if it were freely mounted. This anti-rolling motion is very important, since it prevents plowing of ink to either end of the fountain. If the cone is not caused to rotate in the anti-rolling direction, ink will be plowed or pushed along to the ends of the ink fountain. Plowing is generally defined as pushing or displacing ink to the ends of the ink fountain. This is undesirable because it can result in premature starvation of the metering nip in the center of the ink fountain. In addition, as a result of the plowing, some ink will also climb or be pushed back up the fountain blade, resulting in a higher ink shoreline. Plowing can also result in overflowing of ink at the ends of the fountain.
The cone-type agitator is described in more detail in U.S. Pat. No. 3,848,529 issued Nov. 19, 1974 to H. W. Gegenheimer and U.S. Pat. No. 3,084,025 issued Apr. 9, 1963 to H. W. Gegenheimer. Although the cone shaped ink agitator has proven to be an invaluable accessory on offset lithographic presses, the need to provide the cone with a rotary motion has proven to be an encumbrance. This leads to two disadvantages when used on certain types of presses.
The first of these disadvantages results from the location or placement of the agitator housing body, which houses the traversing mechanism, which is limited by the requirement of imparting a rotary motion to the cone.
The main element of the agitator traversing mechanism consists of a U-shaped section body, mounted parallel to the fountain roller. The body contains rails which retain and guide the cone carriage. An endless chain, driven by an electric motor, causes the carriage to traverse back and forth along the agitator body. The agitator cone is mounted on a shaft which is retained by bearings in the carriage. A gear fastened to the shaft engages a stationary rack mounted within the body. Thus, when the carriage is caused to move by the endless chain, the cone is rotated by the action of the gear rolling along the rack. Although this design is functionally satisfactory, it allows little flexibility in locating the agitator body. In order to provide greater flexibility in agitator body placement several different indirect cone driven arrangements have been attempted.
However, all of the agitator structures have one feature in common; namely, the U-shaped section body is mounted on its side so that the opening in the body faces the fountain.
This arrangement poses a problem on web presses in that the traversing mechanism is exposed to contamination and fouling by ink spillage during both hand feeding and cleaning of the fountain.
The second drawback of the rotary cone design stems from the fact that, even with various design variations, it is not always possible to mount the ink agitator in a location on a press that does not obstruct access to the ink fountain or get in the way of the pressman. This problem is especially acute on both the lower printing units of many web presses and many common impression sheetfed presses.
In addition to the foregoing the cone shaped, traversing, rotating ink agitator cone requires, as indicated above, a relatively large number of parts. Thus the manufacture of such an ink agitator can be expensive. It is also difficult and time consuming to clean in the event it becomes encrusted with ink.
Web presses operate at high speeds and as a result utilize larger than normal amounts of ink and the pressman is constantly replenishing the ink supply with the result that a sloppy pressman can spill ink into the ink agitator's inner workings.